It is created experimental combined optical and infra-red imaging complex, allowing to investigate influence of the relative sizes of a layer on transition to a multiscale Rayleigh-Bénard convection of a liquid in layers with two rigid isothermal surfaces and with free surface under stationary and non-stationary temperature boundary conditions. Visualization of superficial structure of a liquid is carried out by hilbert-optics methods in reflected light. Contactless control of a thickness of a layer of a liquid was carried out by specially developed remote measuring instrument on the basis of microscope MBR -1 with knot of smooth focusing on the basis of Meyer's micromechanism. Chronological photos dynamic changes of relief structure and a temperature field of an investigated liquid are received, besides the results confirming existence of currents in the form of two-dimensional platens with axes of rotation, parallel to lateral borders (cavity walls). It is shown that the current of strongly viscous liquid has the thermal gravitational nature.Correlation of evolution of superficial structures thermogram and hilbert shadow images in various modes of a Rayleigh-Bénard convection is established.